The present invention relates to an automatic load displacement device for the internal combustion engine of an automotive vehicle, wherein the displacement device has a coupling gear driven by a servomotor and held against a coupling lever, the coupling lever being swingable by an electromagnet around an axis against the force of a spring, and wherein the coupling gear engages in coupled condition into a gear wheel which is part of an actuator mechanism which actuates a setting member for setting a level of fuel flow into the engine.
Load displacement devices of the above type are known and customary in commercial vehicles in order to limit the maximum possible speed of the vehicle. By way of example, since the beginning of 1994, a structurally limited maximum speed of 85 km/hr, which can be achieved with such automatic load displacement devices, has even been required by law in Germany for trucks.
The known load displacement devices which operate as a speed limiter are connected by a rod to the injection pump of the diesel engine of the commercial vehicle. When the maximum speed set has been reached, an electronic controller gives a speed reduction command to the servomotor. In this way, the amount of fuel injected is decreased to such an extent by displacement of the injection pump that the speed of the vehicle remains constant. The forces in the actuator mechanism are so selected that upon operation of the servomotor, the coupling lever always holds the coupling gear wheel in engagement with the gear wheel of the actuator mechanism provided that the electromagnet which effects the coupling is acted on by current.
In passenger cars, load displacement devices, are known which make it possible not only to prevent exceeding a desired adjustable limiting speed but, in addition, also prevent a dropping below the set speed. This is accomplished in the manner that a throttle valve is increasingly opened when there is an increased need for power, for instance upon traveling up an incline. The displacement of the actuator member--the throttle valve of an injection pump--therefore takes place in two directions, in contradistinction to the undirectional limiting of the speed in commercial vehicles.
Recently, there has been an increasing desire to provide commercial vehicles also with the possibility of maintaining a desired constant speed which has been found desirable in passenger cars. However, since larger actuating forces must be produced for control of fuel in commercial vehicles than in passenger cars, existing speed control devices cannot be used for this.
The converting of existing speed limiters has also not been possible up to now since the load displacement necessary for speed regulation must take place in two directions and, in the case of speed limiters which are developed only for reducing the speed, the coupling gear wheel is disengaged by tooth repelling forces upon a reversal of the direction of rotation for the increasing of the speed. The reason for this is that the forces on the coupling lever are dependent on the direction of the load, and speed limiters are so designed that with the direction of load which is alone present in them, the tooth-displacement forces do not lead to an uncoupling.
In order to avoid an uncoupling in the load displacement device, the electromagnet which effects the coupling when the ignition is turned on could be made sufficiently strong so that the force produced by the electromagnet sufficiently overcomes the tooth displacement forces of the coupling gear and the gear wheel even in the most unfavorable case. Such an embodiment, however, would have the disadvantage that the electromagnet would produce a relatively large amount of heat which would be injurious for the plastic teeth of the gears of the actuator mechanism. Aside from this, the cost of manufacture would be considerably increased by a strong electromagnet and the structural size of the load displacement device as well as its energy consumption would increase undesirably greatly.